Under-voltage protection circuit for battery

Abstract

An under-voltage protection circuit has a power input terminal connected to a battery, a power output terminal connected to an electronic device, a switch circuit for switching the power supply circuit from the power input terminal to the power output terminal, a control circuit for controlling the switch circuit, and a control voltage generating circuit that generates a first control voltage when the switch circuit is cut off. The control circuit controls the switch circuit in accordance with the first control voltage. The control voltage generating circuit further generates a second control voltage when the switch circuit is conductive, and then the control circuit controls the switch circuit in accordance with the second control voltage.

What is claimed is: 
     
       1. An under-voltage protection circuit, comprising:
 a power input terminal for being connected to a battery; 
 a power output terminal for being connected to an electronic device; 
 a switch circuit for switching a power supply from the power input terminal to the power output terminal; 
 a control circuit for controlling the switch circuit; and 
 a control voltage generating circuit that generates a first control voltage when the switch circuit is cut off, wherein the control circuit controls the switch circuit in accordance with the first control voltage; the control voltage generating circuit further generates a second control voltage when the switch circuit is conducted, wherein the control circuit controls the switch circuit in accordance with the second control voltage; the control voltage generating circuit comprises a first resistor and a second resistor connected in series, and the first control voltage is formed on a node between the first resistor and the second resistor; the control voltage generating circuit further comprises a first switch and a third resistor; when the switch circuit is conducted, the power output terminal feedbacks to the control voltage generating circuit, and control the first switch to be conducted; upon the first switch being conducted, the third resistor connects to the first resistor in parallel and then connected with the second resistor in series to form the second control voltage on the node between the first resistor and the second resistor. 
 
     
     
       2. The under-voltage protection circuit as claimed in  claim 1 , wherein the first switch is a nMOSFET, and the power output terminal feedbacks to a gate of the first switch to control the first switch; a drain of the first switch is connected to the power input terminal, and a source of the first switch is connected to the node between the first resistor and the second resistor.